Conventionally, a track ball assembly includes a cover, a ball, a housing to admit the ball, a plurality of ball bearings which are evenly distributed around an inner surface of the housing to support the ball, a seat having locking means thereon and an encoder wheel which is incorporated with a photoemitter as well as a photodetector together to form a detecting system to control the movement of a visual cursor on a monitor.
But some disadvantages exist in the aforementioned design. First, the thorough base structure assembly consisting of a housing and a seat to hold the encoder wheel and the ball is accomplished by linking several parts and may suffer damages from any mistake trying to interconnect each part. Second, it is known that the ball bearing is kept partially inside a hole in order to provide an anti-friction interface to support and permit the ball rotate freely in the housing. But, the problem is the whole ball bearing will be pushed down into the hole and then get jammed if acted upon by a excessive force. Third, the encoder wheel and the housing are connected together to the seat by spring biasing means while this arrangement is cumbersome. Finally, a block on which a photoemitter and a photodetector are located in pair is only releasably engaged with the seat.